Systems that identify video images and/or sequences of video images (e.g., television commercials or programs) being broadcast and/or viewed on an output device (e.g., a television or video monitor) are often used to verify that certain audio and/or video content or programs (e.g., television programs, advertisements, etc.) have been broadcast in particular geographic regions at particular times. Of course, such video identification system may additionally or alternatively be used to facilitate the analysis of viewing behaviors of selected groups of viewers. Some video identification systems identify programs by extracting audio and/or video information associated with a program currently being broadcast and/or viewed and processing that extracted information to generate audio and/or video signatures. Typically, the audio and/or video signatures are digital sequences or codes that, at a given instant of time, are substantially unique to each portion of audio/video content or program. In this manner, an unidentified video program can be reliably identified by finding a matching signature within a database or library containing the signatures of known available programs. When a matching signature is found, the previously unidentified audio/video content (e.g., television program, advertisement, etc.) is identified as the one of the known available programs corresponding to the matching database signature.
Video signatures may be generated for analog and/or digital video programs. Some known video signature generation techniques for use with digital video program information process some or all of the uncompressed image data for one or more video frames to generate one or more signatures for the video program associated with the video frames. However, using uncompressed video data to generate signature information usually requires expensive high-speed signature generation hardware or circuitry, or software/processor-based signature generation techniques that result in relatively slow signature generation rates. For some applications, such as, for example, television audience viewing behavior analysis or other program verification or identification systems that use data acquisition and signature generation devices, high speed hardware-based video signature generation systems are cost prohibitive. In addition, many software-based signature generation systems are too slow and may miss important verification and/or viewing information such as, for example, relatively short television commercials or the like.
In some software-based systems, the speed at which video signatures are generated may be increased by using less video information (e.g., fewer frames, smaller portions of each frame, etc.) to generate the signature information. However, the use of less information usually results in a signature that is less likely to uniquely represent the associated video content, thereby resulting in an increased false match rate (i.e., incorrectly identifying a video program) and an increased failure to find a match when a match exists (i.e., the failure to identify a known video program).
Still further, the video signature generation systems used with many video program identification systems are not independent of image format or encoder operation. For example, changing the display aspect ratio (e.g., from 4:3 to 16:9) for a video program may significantly change the video signature information generated therefrom. As a result, while these known systems may be able to reliably identify a group of known images/frames and, thus, known programs when formatted for a 4:3 aspect ratio display, these same systems may fail to identify any of those known programs when formatted using a different aspect ratio. Similarly, many of these known systems are also sensitive to video program frame rate (e.g., the number of frames per second that compose a video program). For example, while many known systems may be able to reliably identify video programs that are composed of frames or images that are to be displayed at a rate of thirty frames per second, those same systems may be unable to identify those same programs when composed of more or fewer frames or images per second.